This application is based on and claims priority to Japanese Patent Application No. 11-245110, filed Aug. 31, 1999, the entire contents of which is hereby expressly incorporated by reference.
1. Field of the Invention
This invention relates to a catalyzer arrangement, and more particularly to an improved catalyzer arrangement suitable to an outboard motor.
2. Description of Related Art
A typical outboard motor has an engine atop thereof for powering a propulsion device. A protective cowling surrounds the engine. The engine and protective cowling together define the power head of the outboard motor. A driveshaft housing depends from the power head for supporting a driveshaft that extends from a crankshaft of the engine. A lower unit depends from the driveshaft housing for carrying the propulsion device, such as, for example, a propeller that is driven by the driveshaft through the propulsion shaft. The engine is provided with an exhaust system to discharge exhaust gases from the motor.
A typical exhaust system includes generally three exhaust passages. The first passage is disposed within the engine or on the engine and within the protective cowling to lead the exhaust gases from the engine. The second passage is disposed within the driveshaft housing and the lower unit for guiding the exhaust gases to the third passage and also for silencing exhaust noise by passing the exhaust gases through at least one expansion chamber. The third passage is defined within a hollow hub of the propeller and terminates at a discharge port formed at the end of the hub. Normally, an idle exhaust passage with an idle discharge port is additionally provided in the driveshaft housing above the body of water that surrounds the outboard motor. The majority of the exhaust gases are discharged to the body of water through the discharge port of the propeller hub, while the idle exhaust gases are discharged to the atmosphere through the idle discharge port.
It is quite important for environmental concerns to remove hydrocarbons and the like from exhaust gases. For at least this reason, the exhaust gases often are purified with a catalyzer that is disposed within the exhaust system. The catalyzer includes components that chemically react with the exhaust gases in a manner that renders certain of the exhaust gas constituents substantially environmentally harmless. The larger the catalyzer is, the greater its efficiency is; however, because the engine is surrounded by the protective cowling, space is at a premium and limited areas are available for positioning the catalyzer. If the engine has multiple cylinder bores, properly positioning the catalyzer becomes more difficult. Moreover, if a large single catalyzer or small multiple catalyzers are used to treat exhaust gases coming from the respective cylinder bores, finding adequate space within the cramped confines of the cowling becomes very difficult.
In one arrangement, such as that disclosed by U.S. Pat. No. 5,239,825, a catalyzer arrangement for a multiple cylinder engine features a single catalyzer that is disposed in the first exhaust passage and sideward of the engine. Although the arrangement is compact, the catalyzer is somewhat bulky.
U.S. Pat. No. 5,378,180 discloses another arrangement in which a catalyzer is disposed also in the first exhaust passage but rearward of an engine. This type of arrangement, however, requires a large amount of space rearward of the engine. It is undesirable to expand the motor rearward because such a construction would make handling of the motor more difficult. Additionally, if the engine operates on a four-stroke combustion principle, a voluminous valve system is disposed in this space and consumes a majority of the available area.
U.S. Pat. Nos. 5,174,112 and 5,280,708 disclose further arrangements of catalyzers. The catalyzers in these patents are disposed in the second exhaust passages that are positioned within the driveshaft housing. Although a relatively large capacity is available with the catalyzer in this arrangement, the catalyzer is likely positioned proximate the water line. As is known, catalyzers can be fouled or shattered by contact with water. Accordingly, positioning the catalyzers proximate the water line is disadvantageous due to the possibility of water back flow through the exhaust system. Thus, catalyzers preferably are positioned well above the water line or the exhaust system preferably includes a shelter that can protect the catalyzers from water contact.
A need therefore exists for an improved catalyzer arrangement that does not require a large space for furnishing a catalyzer that has a relatively large volume, and that does not expose the catalyzer toward the body of water without any particular protection.
In accordance with one aspect of the present invention, an outboard motor comprises an internal combustion engine. The engine includes a first exhaust section. A driveshaft housing is adapted to be mounted on an associated watercraft. A support member is mounted on the driveshaft housing for supporting the engine above the driveshaft housing. An exhaust unit is disposed to the side of the support member. The exhaust unit defines a second exhaust section coupled to the first exhaust section. A catalyzer is disposed in the second exhaust section.
In accordance with another aspect of the present invention, an outboard motor comprises an internal combustion engine. The engine includes a first exhaust section. A driveshaft housing is adapted to be mounted on an associated watercraft. A support member is mounted on the driveshaft housing for supporting the engine. An exhaust unit is mounted on the support member. The exhaust unit defines a second exhaust section coupled to the first exhaust section. A catalyzer is disposed in the second exhaust section.
In accordance with a further aspect of the present invention, an exhaust gas purifying system is provided for an outboard motor. The outboard motor has an internal combustion engine and a support member supporting the engine. The exhaust gas purifying system comprises a first exhaust section. The first exhaust section extends through both the engine and the support member. A second exhaust section is coupled to the first exhaust section and extends out of the support member. A third exhaust section is coupled to the second exhaust section and extends through the support member. A catalyzer is disposed in the second exhaust section.
Further aspects, features and advantages of this invention will become apparent from the detailed description of the preferred embodiments which follow.